Networks may be independently present, and such independent networks may be multiple networks, such as a first network, a second network, and a third network.
However, in a state in which first and second networks are independent, the sending/receiving of mails between both the networks is impossible, and contents and files corresponding to mails created in the first network must be moved to the second network through a separate storage medium, and must be used to perform a task. In particular, when the contents of a mail created in the first network are linked to a third network, it is impossible to utilize or read the mail in the second network. Further, when it is desired to read a mail, created in the second network, in the first network, there is inconvenience in that the mail must be moved from the second network to the first network through a separate portable storage medium before it can be read.
Further, there is inconvenience in that when it is desired to download data from the first network and utilize the data in the second network, the data must be moved to the second network through a separate portable storage medium.
Meanwhile, there is inconvenience in that images and text of the first network must be stored in the form of a file using a separate screen capture system and must be moved to and utilized in the second network through a separate portable storage medium.
In this way, in the environment in which networks are independent, the transfer of data between both networks must be performed using a separate portable storage medium, management procedures, such as for carrying-in/carrying-out of the storage medium and regulation of the use of an unauthorized storage medium, must be involved, and the performance of storage and transfer of data is completely dependent on the determination of a user, thus causing a possibility that data may be leaked due to the carelessness of the user. Further, a problem arises in that due to abrasion and damage to a storage medium caused by long-term use of the storage medium, important task data may be lost.
Furthermore, in an environment in which networks are independent, screen capturing, keylogging, etc. are blocked and a drag & drop operation, a copy & paste operation, etc. for data are prevented between both independent networks, thus causing inconvenience in use.